The present invention relates to cooling fans such as fans used in connection with an automotive or industrial cooling system. More specifically, the invention pertains to fans with integral blades formed in a molding process, such as an injection molding procedure.
Most automotive and industrial power components require some form of auxiliary cooling system. In a typical automotive application, this cooling system includes a radiator and a cooling fan that directs air across the radiator. In these applications, the fan is mounted to a rotating flange of a fan drive that is separate from the power plant output.
In the early design of such cooling fans, metal blades were mounted to a metal hub, which hub was then attached to the fan drive. In recent years, however, high-strength polymer materials have been used to form various components of the fan. The polymer fan design was found to be capable of withstanding the normal forces and stresses endured by a cooling fan in even the heaviest duty automotive or industrial application. Moreover, the use of polymer materials provided a significant reduction in weight of the cooling fan. Moreover, and perhaps most significantly, the use of polymers generated significant benefits in the manufacture of the fan, since materials of this type readily lend themselves to a variety of molding processes.
The one-piece molded fan has eliminated the welds and rivets commonly associated with prior metal fans. In addition, the molding process facilitated the generation of smooth rounded contours, which ultimately reduced internal stresses within the fan structure.
In one type of molded fan design, the entire fan and hub are formed in a single piece. An example of this form of a one-piece molded fan is shown in U.S. Pat. No. 4,671,739 to Read et al. Fans of this type were found to be better suited for smaller duty applications, such as for use in the cooling system of passenger automobiles. For larger, higher stress applications, a hubless molded fan design was found to be more appropriate. One such design is depicted in U.S. Pat. No. 5,593,283 to Scott. In this design, a polymer hubless fan is integrally formed around a metallic mounting hub. This mounting hub can be supported within the molding apparatus, such as a typical injection molding machine. The polymer material is then injected into a mold surrounding the hub to form an interlocking ring around the metal hub.
In many automotive and industrial applications the molded fan includes a polymer, such as polypropylene, nylon or other resin compositions. In addition, many industrial fans include reinforcing material such as glass fibers or nylon strands. The reinforcing material can be oriented within the structure of the molded fan blade to provide additional strength and stiffness where needed based upon stress analysis of the working fan.
The hubless fan design has evolved since its inception. While the metal mounting hub provides a certain degree of strength to the overall fan, the molded fan can include an enlarged polymer ring formed around the mounting hub. This ring helps provides strength and bending or flexure stiffness to the root of each of the fan blades.
While the hubless polymer fan represents an improvement over prior metal and one-piece polymer fan constructions, improvements are still needed. For instance, cost and material considerations are implicated by current molded fan designs involving significant material waste. Cost considerations are also involved in the storing and shipping of an inventory of fans. There remains a need for a molded fan assembly that reduces the overall costs associated with manufacturing and shipping the final fan product.
In order to address the needs unmet by prior fan designs, the present invention contemplates a fan assembly comprising a substantially rigid hub configured for mating with a fan drive and defining a perimetrical flange. A hubless fan includes a circumferential ring molded about the perimetrical flange of the rigid hub, and a plurality of outwardly projecting fan blades integrally formed with the ring.
In one embodiment of the invention, the hubless fan further includes a plurality of hot runners for introduction of molten material into the hubless fan that are radially disposed between the circumferential ring and the root diameter of the fan blades. With this feature, molten polymer material is distributed more uniformly throughout the molded hubless fan. Moreover, less material is wasted in the form of a cold sprue that must be trimmed from the completed fan assembly. In a further aspect, each of the hot runners is raised relative to the circumferential ring, which allows the hot runners to have a larger diameter to accept greater flow of molten material into the hubless fan mold.
In a further embodiment of the invention, the circumferential ring of the hubless fan defines a plurality of bores dispersed about the circumference of the ring. Each of the bores is configured for receiving a balance weight therein. In the most preferred embodiment, the balance weight is in the form of a screw having a known weight and including self-tapping threads for screwing into a specific one of the bores. The ring defines a predetermined number of the bores radially aligned with a corresponding one of the fan blades, namely four such bores in the most preferred embodiment. Standard rotating body balancing techniques can be used to determine the magnitude of weight and the boss location for the addition of the balancing screw.
In another aspect of this inventive feature, the circumferential ring includes a plurality of raised bosses in which each of the bosses includes a corresponding one of the plurality of bores. The bosses have a height from the circumferential ring, and the bores have a depth no greater than that height to avoid compromising the body of the circumferential ring supporting the fan blades. A stiffening ring is formed between and interconnecting adjacent ones of the plurality of raised bosses that has a height substantially equal to the raised height of the bosses.
The present invention also provides a feature to enhance the stackability of the fan assemblies. In another aspect of the invention, the stiffening ring defines at least two recessed flats between a corresponding adjacent pair of raised bosses. The stiffening ring has a reduced height at each of the recessed flats that is less than the height of the stiffening ring of bosses. On the opposite face of the hubless fan, the circumferential ring further includes at least two raised tabs projecting therefrom. Each of the tabs is sized and arranged to reside within a corresponding one of the recessed flats. Thus, when two or more of the hubless fans are stacked, the raised tabs of one of the fans nests within corresponding ones of the recessed flats of an adjacent one of the hubless fans.
In a preferred embodiment, the number of raised tabs and recessed flats equals the number of fan blades. The tabs and flats can be situated in radial alignment with the gap between adjacent fan blades.
It is one object of the present invention to provide a fan assembly utilizing a hubless fan that minimizes the amount of material required to form the fan in a molding process. Reducing the amount of material waste is also accomplished by features of the invention that eliminate the need to trim blade material for balancing the fan assembly.
Another object of the invention is directed to improving the stackability of molded fan assemblies. An added object resides in features that enhance the stability of a stack of such fan assemblies.
Other objects and particular benefits of the invention will become apparent to a person of skill in this art upon consideration of the following written description and accompanying figures.